We currently use our ISP's smarthost for sending out automated noreply emails from our system. We are sending around 20000 emails a day and the ISP has asked us to sort out our own MTA as the load is getting a little high for their comfort. Current SMTP Connector is installed on Server 2003 and forwards all email sent to it from our daemons to a external smarthost.
I am looking for recommendations of what would be the best replacement solution.
There is no need for receiving incoming email.
Currently I am considering each of the following,
1. MS Virtual SMTP Server Connector as MTA - it is currently using this to forward to the smarthost
2. Install Postfix on a Linux server and use this as a smarthost
3. Use an third party provider's smarthost in the same way we are using our ISP's at the moment
My main concerns for each are the following:
Would it support sending 20000 emails a day?
Would you recommend SPF record for sending domain to decrease change false positives (SPAM)?
Can DKIM be configured on each?
Which methods are more prone to blacklisting assuming they haven't been comprimised?
This is a mission critical service and it needs to work. If sending domain or IP is blacklisted or filtered by any other servers it would be disastrous. Due to this my main prerequisite is reliability.
Could anyone with experience please give me their opinion?